<template>
  <!-- 歌曲列表页面 -->
  <div class="music-list">
    <div class="back" @click="back">
        <i class="icon-back"/>
    </div>
    <h1 class="title">{{title}}</h1>
    <!-- 歌手海报 -->
    <div class="bg-image" :style="bgStyle" ref="bgImage">
      <div class="play-wrapper">
        <div class="play" ref="playBtn" v-show="songsList.length" @click="random">
          <i class="icon-play"></i>
          <span class="text">随机播放全部</span>
        </div>
      </div>
      <!-- 歌手海报蒙层 -->
      <div class="filter" ref="filter"/>
    </div>
    <!-- 背景层 -->
    <div class="bg-layer" ref="layer"></div>
    <!-- 歌曲列表 -->
    <scroll
      class="list"
      ref="list"
      @scroll="scroll"
      :listen-scroll="listenScroll"
      :data="songsList"
      :probe-type="probeType"
    >
      <div class="song-list-wrapper">
        <song-list :songsList="songsList" @select="selectItem"/>
      </div>
      <!-- loading -->
      <div v-show="!songsList.length" class="loading-container">
        <loading></loading>
      </div>
    </scroll>
  </div>
</template>

<script>
import SongList from '../songList/SongList'
import Scroll from '../scroll/Scroll'
import Loading from '../loading/Loading'
import { prefixStyle } from '../../assets/js/dom'
import { playlistMixin } from '../../assets/js/mixin'
import { mapActions } from 'vuex'

const RESERVED_HEIGHT = 40
const transform = prefixStyle('transform')
const backdropFilter = prefixStyle('backdrop-filter')

export default {
  name: 'musicList',
  mixins: [playlistMixin],
  props: {
    title: {
      type: String,
      default: ''
    },
    avatar: {
      type: String,
      default: ''
    },
    songsList: {
      type: Array,
      default: () => []
    }
  },
  data () {
    return {
      scrollY: 0 // 在data中列出属性，才可以被watch中的方法监控
    }
  },
  created () {
    this.probeType = 3
    this.listenScroll = true
  },
  mounted () {
    this.imageHeight = this.$refs.bgImage.clientHeight // 图片高度
    this.minTransalteY = -this.imageHeight + RESERVED_HEIGHT // 背景层最小偏移量
    this.$refs.list.$el.style.top = `${this.imageHeight}px` // 计算出滚动容器的顶部位置
  },
  computed: {
    bgStyle () {
      return { backgroundImage: `url(${this.avatar})` }
    }
  },
  methods: {
    handlePlaylist (playlist) {
      const bottom = playlist.length > 0 ? '60px' : ''
      this.$refs.list.$el.style.bottom = bottom
      this.$refs.list.refresh()
    },
    back () {
      this.$router.back()
    },
    scroll (pos) {
      this.scrollY = pos.y
    },
    selectItem (item, index) {
      this.selectPlay({
        list: this.songsList,
        index
      })
    },
    random () {
      this.randomPlay({
        list: this.songsList
      })
    },
    ...mapActions(['selectPlay', 'randomPlay'])
  },
  watch: {
    scrollY (newVal) {
      let zIndex = 0
      // 遮罩层向上偏移
      let translateY = Math.max(this.minTransalteY, newVal)
      this.$refs.layer.style[transform] = `translate3d(0,${translateY}px,0)`
      // 背景图片模糊
      let blur = 0
      let scale = 1
      const percent = Math.abs(newVal / this.imageHeight)
      if (newVal < 0) {
        blur = Math.min(20, percent * 20)
      } else {
        scale = 1 + percent
        zIndex = 10 // 海报遮盖歌曲列表
      }
      this.$refs.filter.style[backdropFilter] = `blur(${blur}px)`
      this.$refs.bgImage.style[transform] = `scale(${scale})`
      // 背景图片尺寸、随机播放按钮显示/隐藏
      if (newVal < this.minTransalteY) {
        zIndex = 10
        this.$refs.bgImage.style.paddingTop = 0
        this.$refs.bgImage.style.height = `${RESERVED_HEIGHT}px`
        this.$refs.playBtn.style.display = 'none'
      } else {
        this.$refs.bgImage.style.paddingTop = '70%'
        this.$refs.bgImage.style.height = 0
        this.$refs.playBtn.style.display = ''
      }
      this.$refs.bgImage.style.zIndex = zIndex
    }
  },
  components: {
    Scroll,
    SongList,
    Loading
  }
}

</script>
<style lang='stylus' scoped>
@import '~@/assets/stylus/variable'
@import '~@/assets/stylus/mixin'
.music-list
  position: fixed
  z-index: 100
  top: 0
  left: 0
  bottom: 0
  right: 0
  background: $color-background
  .back
    position: absolute
    top: 0
    left: 6px
    z-index: 50
    .icon-back
      display: block
      padding: 10px
      font-size: $font-size-large-x
      color: $color-theme
  .title
    position: absolute
    top: 0
    left: 10%
    z-index: 40
    width: 80%
    no-wrap()
    text-align: center
    line-height: 40px
    font-size: $font-size-large
    color: $color-text
  .bg-image
    position: relative
    width: 100%
    height: 0
    padding-top: 70%
    transform-origin: top
    background-size: cover
    .play-wrapper
      position: absolute
      bottom: 20px
      z-index: 50
      width: 100%
      .play
        box-sizing: border-box
        width: 135px
        padding: 7px 0
        margin: 0 auto
        text-align: center
        border: 1px solid $color-theme
        color: $color-theme
        border-radius: 100px
        font-size: 0
        .icon-play
            display: inline-block
            vertical-align: middle
            margin-right: 6px
            font-size: $font-size-medium-x
        .text
            display: inline-block
            vertical-align: middle
            font-size: $font-size-small
    .filter
      position: absolute
      top: 0
      left: 0
      width: 100%
      height: 100%
      background: rgba(7, 17, 27, 0.4)
  .bg-layer
    position: relative
    height: 100%
    background: $color-background
  .list
    position: absolute
    top: 0
    bottom: 0
    width: 100%
    background: $color-background
    .song-list-wrapper
      padding: 20px 30px
    .loading-container
      loading-content()
</style>
